U.S. patent application number 13/099959 was filed with the patent office on 2012-11-08 for verification of pressure metrics.
This patent application is currently assigned to Medtronic, Inc.. Invention is credited to Tommy D. Bennett, Yong Kyun Cho, William J. Havel, Robert T. Taepke, II.
Application Number | 20120283580 13/099959 |
Document ID | / |
Family ID | 46147704 |
Filed Date | 2012-11-08 |
United States Patent
Application |
20120283580 |
Kind Code |
A1 |
Havel; William J. ; et
al. |
November 8, 2012 |
VERIFICATION OF PRESSURE METRICS
Abstract
An example system may include at least one pressure sensor
configured to measure a cardiovascular pressure signal and another
medical device configured to measure an electrical depolarization
signal of the heart. The system determines a plurality of
cardiovascular pressure metrics based on the measured
cardiovascular pressure signal, including at least one
cardiovascular pressure metric indicative of a timing of at least
one cardiac pulse. The system also determines a metric indicative
of a timing of at least one heart depolarization within the
measured electrical depolarization signal. The system compares the
timing of the at least one cardiac pulse to the timing of the at
least one depolarization, and determines whether to discard the
plurality of cardiovascular pressure metrics based on whether the
timings substantially agree.
Inventors: |
Havel; William J.; (Maple
Grove, MN) ; Bennett; Tommy D.; (Shoreview, MN)
; Cho; Yong Kyun; (Maple Grove, MN) ; Taepke, II;
Robert T.; (Coon Rapids, MN) |
Assignee: |
Medtronic, Inc.
Minneapolis
MN
|
Family ID: |
46147704 |
Appl. No.: |
13/099959 |
Filed: |
May 3, 2011 |
Current U.S.
Class: |
600/485 |
Current CPC
Class: |
A61B 5/7207 20130101;
A61N 1/3702 20130101; A61B 5/0215 20130101; A61B 5/686 20130101;
A61N 1/36564 20130101; A61B 5/7239 20130101 |
Class at
Publication: |
600/485 |
International
Class: |
A61B 5/021 20060101
A61B005/021 |
Claims
1. A method comprising: measuring, by a pressure sensor, a
cardiovascular pressure signal; determining a plurality of
cardiovascular pressure metrics based on the measured
cardiovascular pressure signal, wherein the plurality of
cardiovascular metrics includes at least one cardiovascular
pressure metric indicative of a timing of at least one cardiac
pulse; measuring, by a medical device that is coupled to the
pressure sensor, an electrical depolarization signal of the heart;
determining a metric indicative of a timing of at least one heart
depolarization based on the measured electrical depolarization
signal; comparing the timing of the at least one cardiac pulse to
the timing of the at least one heart depolarization; and
determining whether to discard the plurality of cardiovascular
pressure metrics based on whether the timings substantially
agree.
2. The method of claim 1, wherein the metric indicative of a timing
of at least one heart depolarization comprises a heart rate and the
at least one cardiovascular pressure metric indicative of a timing
of at least one cardiac pulse comprises a pulse rate.
3. The method of claim 1, wherein the pressure sensor is wirelessly
coupled to the medical device.
4. The method of claim 1, further comprising: transmitting the
plurality of cardiovascular pressure metrics from the pressure
sensor to the medical device.
5. The method of claim 1, further comprising: transmitting the
metric indicative of a timing of at least one heart depolarization
from the medical device to the pressure sensor.
6. The method of claim 5, wherein the metric indicative of a timing
of at least one heart depolarization is transmitted wirelessly.
7. The method of claim 1, further comprising: re-measuring, by the
pressure sensor, the cardiovascular pressure signal in response to
discarding the plurality of cardiovascular pressure metrics;
determining plurality of cardiovascular pressure metrics based on
the re-measured cardiovascular pressure signal, wherein the
plurality of cardiovascular metrics includes the at least one
cardiovascular pressure metric indicative of the timing of at least
one cardiac pulse; re-measuring, by the medical device that is
coupled to the pressure sensor, the electrical depolarization
signal of the heart; determining the metric indicative of a timing
of at least one heart depolarization based on the re-measured
electrical depolarization signal; comparing the timing of the at
least one cardiac pulse to the timing of the at least one heart
depolarization; and determining whether to discard the plurality of
cardiovascular pressure metrics based on whether the timings
substantially agree.
8. The method of claim 7, further comprising: determining a number
of times that the cardiovascular pressure signal has been
re-measured in response to discarding the plurality of
cardiovascular pressure metrics; comparing the number of times that
the cardiovascular pressure signal has been re-measured to a
predetermined threshold; and determining whether to re-measure the
cardiovascular pressure signal based on the comparison.
9. The method of claim 1, wherein, in addition to the
cardiovascular pressure metric indicative of a timing of at least
one cardiac pulse, the plurality of cardiovascular pressure metrics
include at least one of a systolic pressure and a diastolic
pressure.
10. The method of claim 1, wherein the medical device is an
external monitoring device.
11. The method of claim 1, wherein the medical device is an
implantable medical device.
12. The method of claim 11, wherein the medical device is implanted
subcutaneously.
13. A system comprising: at least one pressure sensor configured to
measure a cardiovascular pressure signal; an medical device
configured to measure an electrical depolarization signal of the
heart; at least one analysis module configured to: determine a
plurality of cardiovascular pressure metrics based on the measured
cardiovascular pressure signal, wherein the plurality of
cardiovascular metrics includes at least one cardiovascular
pressure metric indicative of a timing of at least one cardiac
pulse; and determine a metric indicative of a timing of at least
one heart depolarization based on the measured electrical
depolarization signal; and at least one processor configured to:
compare the timing of the at least one cardiac pulse to the timing
of the at least one heart depolarization; and determine whether to
discard the plurality of cardiovascular pressure metrics based on
whether the timings substantially agree.
14. The system of claim 13, wherein the metric indicative of a
timing of at least one heart depolarization comprises a heart rate
and the at least one cardiovascular pressure metric indicative of a
timing of at least one cardiac pulse comprises a pulse rate.
15. The system of claim 13, wherein the at least one pressure
sensor is a wirelessly coupled to the medical device.
16. The system of claim 15, wherein the pressure sensor is
configured to wirelessly transmit the plurality of cardiovascular
metrics to the medical device.
17. The system of claim 13, wherein the processor is configured to
control the pressure sensor to re-measure the cardiovascular
pressure signal if the plurality of cardiovascular pressure metrics
is discarded.
18. The system of claim 17, wherein the processor is configured to:
determine a number of times that the cardiovascular pressure signal
has been re-measured in response to discarding the plurality of
cardiovascular pressure metrics; compare the number of times that
the cardiovascular pressure signal has been re-measured to a
predetermined threshold; and determine whether to control the
pressure sensor to re-measure the cardiovascular pressure signal
based on the comparison.
19. The system of claim 13, wherein, in addition to the
cardiovascular pressure metric indicative of a timing of at least
one cardiac pulse, the plurality of cardiovascular pressure metrics
include at least one of a systolic pressure and a diastolic
pressure.
20. The system of claim 13, wherein the medical device comprises
the processor.
21. The system of claim 13, wherein the medical device is
configured for subcutaneous implantation within a patient.
22. A system comprising: means for measuring a cardiovascular
pressure signal; means for measuring an electrical depolarization
signal of the heart; means for determining a plurality of
cardiovascular pressure metrics based on the measured
cardiovascular pressure signal, wherein the plurality of
cardiovascular metrics includes at least one cardiovascular
pressure metric indicative of a timing of at least one cardiac
pulse; means for determining a metric indicative of a timing of at
least one heart depolarization within the measured electrical
depolarization signal; means for comparing the timing of the at
least one cardiac pulse to the timing of the at least one
depolarization signal; and means for determining whether to discard
the plurality of cardiovascular pressure metrics based on whether
the timings substantially agree.
23. The system of claim 22, wherein the metric indicative of a
timing of at least one heart depolarization comprises a heart rate
and the at least one cardiovascular pressure metric indicative of a
timing of at least one cardiac pulse comprises a pulse rate.
24. A method comprising: measuring, by a first pressure sensor, a
first cardiovascular pressure signal; determining a plurality of
first cardiovascular pressure metrics based on the measured first
cardiovascular pressure signal, wherein the plurality of first
cardiovascular metrics includes at least one first cardiovascular
pressure metric indicative of a timing of at least one cardiac
pulse; measuring, by a second pressure sensor that is coupled to
the first pressure sensor, a second cardiovascular pressure signal;
determining at least one second cardiovascular pressure metric
based on the measured second cardiovascular pressure signal,
wherein the at least one second cardiovascular pressure metric is
indicative of a timing of at least one cardiac pulse; comparing the
timing of the at least one cardiac pulse indicated by the first
cardiovascular pressure metric to the timing of the at least one
cardiac pulse indicated by the second cardiovascular pressure
metric; and determining whether to discard the plurality of first
cardiovascular pressure metrics based on whether the timings
substantially agree.
25. The method of claim 24, wherein the first pressure sensor is
located outside of the heart and the second pressure sensor is
located within the heart.
26. A system comprising: a first pressure sensor configured to
measure a first cardiovascular pressure signal; a second pressure
sensor configured to measure a second cardiovascular pressure
signal, wherein the first and second pressure sensors communicate
with each other; and one or more analysis modules implemented in
one or more of the first and second pressure sensors configured to:
determine a plurality of first cardiovascular pressure metrics
based on the measured first cardiovascular pressure signal, wherein
the plurality of first cardiovascular metrics includes at least one
first cardiovascular pressure metric indicative of a timing of at
least one cardiac pulse; determine at least one second
cardiovascular pressure metric based on the measured second
cardiovascular pressure signal, wherein the at least one second
cardiovascular pressure metric is indicative of a timing of at
least one cardiac pulse; compare the timing of the at least one
cardiac pulse indicated by the first cardiovascular pressure metric
to the timing of the at least one cardiac pulse indicated by the
second cardiovascular pressure metric; and determine whether to
discard the plurality of first cardiovascular pressure metrics
based on whether the timings substantially agree.
27. A method comprising: measuring, by a medical device that is
coupled to a pressure sensor, an electrical depolarization signal
of the heart; detecting asystole based on the electrical
depolarization signal of the heart; and in response to the
detection of asystole, directing the pressure sensor to measure a
cardiovascular pressure signal.
28. A system comprising: a pressure sensor; and a medical device
configured to: measure an electrical depolarization signal of the
heart; detect asystole based on the electrical depolarization
signal of the heart; and in response to the detection of asystole,
directing the pressure sensor to measure a cardiovascular pressure
signal.
Description
TECHNICAL FIELD
[0001] The disclosure relates to medical devices and, more
particularly, to implantable medical devices that monitor
cardiovascular pressure.
BACKGROUND
[0002] A variety of implantable medical devices for delivering a
therapy and/or monitoring a physiological condition have been
clinically implanted or proposed for clinical implantation in
patients. Implantable medical devices may deliver electrical
stimulation or drug therapy to, and/or monitor conditions
associated with, the heart, muscle, nerve, brain, stomach or other
organs or tissue, as examples. Implantable medical devices may
include or be coupled to one or more physiological sensors, which
may be used in conjunction with the device to monitor signals
related to various physiological conditions from which a patient
state or the need for a therapy can be assessed.
[0003] Some implantable medical devices may employ one or more
elongated electrical leads carrying stimulation electrodes, sense
electrodes, and/or other sensors. Implantable medical leads may be
configured to allow electrodes or other sensors to be positioned at
desired locations for delivery of stimulation or sensing. For
example, electrodes or sensors may be carried at a distal portion
of a lead. A proximal portion of the lead may be coupled to an
implantable medical device housing, which may contain circuitry
such as stimulation generation and/or sensing circuitry. Other
implantable medical devices may employ one or more catheters
through which the devices deliver a therapeutic fluid to a target
site within a patient. Examples of such implantable medical devices
include heart monitors, pacemakers, implantable cardioverter
defibrillators (ICDs), myostimulators, neurostimulators,
therapeutic fluid delivery devices, insulin pumps, and glucose
monitors.
[0004] Pressure sensors may be employed in conjunction with
implantable medical devices as physiological sensors configured to
detect changes in blood pressure. Example pressure sensors that may
be useful for measuring blood pressure may employ capacitive,
piezoelectric, piezoresistive, electromagnetic, optical,
resonant-frequency, or thermal methods of pressure
transduction.
SUMMARY
[0005] In general, this disclosure describes techniques for
verifying cardiovascular pressure metrics obtained by monitoring a
cardiovascular pressure signal. These verification techniques may
include determining a first cardiovascular pressure metric, such as
a cardiac pulse interval or rate, from a cardiovascular pressure
signal detected by a pressure sensor implanted within the
circulatory system of a patient. The verification techniques may
further include comparing the first cardiovascular pressure metric
to a corresponding cardiac electrical metric, such as a cardiac
depolarization interval or rate, obtained from measuring an
electrical depolarization signal of the heart. In some examples,
the verification techniques may include comparing the first
cardiovascular pressure metric to a corresponding second
cardiovascular pressure metric, such as a second pulse interval or
rate, obtained by monitoring a second pressure signal.
[0006] Agreement between the pressure metric and the electrical
metric, or between two pressure metrics, may provide an indicium of
the reliability of one or more other cardiovascular pressure
metrics determined based on a measured cardiovascular pressure
signal. Using the techniques of this disclosure, a medical device
may more reliably deliver drug therapy or therapeutic electrical
stimulation, or acquire diagnostic information, based on various
pressure metrics determined from a cardiovascular pressure signal.
The techniques of this disclosure may also avoid the use of
communication bandwidth and power consumption that a direct and/or
continuous comparison of the raw cardiovascular pressure signal and
the electrical depolarization signal of the heart may require.
[0007] In one example, a method comprises measuring, by a pressure
sensor, a cardiovascular pressure signal, and determining a
plurality of cardiovascular pressure metrics based on the measured
cardiovascular pressure signal, wherein the plurality of
cardiovascular metrics includes at least one cardiovascular
pressure metric indicative of a timing of at least one cardiac
pulse. The method further comprises measuring, by a medical device
that is coupled to the pressure sensor, an electrical
depolarization signal of the heart, and determining a metric
indicative of a timing of at least one heart depolarization based
on the measured electrical depolarization signal. The method
further comprises comparing the timing of the at least one cardiac
pulse to the timing of the at least one heart depolarization, and
determining whether to discard the plurality of cardiovascular
pressure metrics based on whether the timings substantially
agree.
[0008] In another example, a system comprises at least one pressure
sensor configured to measure a cardiovascular pressure signal, and
a medical device configured to measure an electrical depolarization
signal of the heart. The system further comprises at least one
analysis module configured to determine a plurality of
cardiovascular pressure metrics based on the measured
cardiovascular pressure signal, wherein the plurality of
cardiovascular metrics includes at least one cardiovascular
pressure metric indicative of a timing of at least one cardiac
pulse, and determine a metric indicative of a timing of at least
one heart depolarization based on the measured electrical
depolarization signal. The system further comprises at least one
processor configured to compare the timing of the at least one
cardiac pulse to the timing of the at least one heart
depolarization, and determine whether to discard the plurality of
cardiovascular pressure metrics based on whether the timings
substantially agree.
[0009] In another example, a system comprises means for measuring a
cardiovascular pressure signal, means for measuring an electrical
depolarization signal of the heart, means for determining a
plurality of cardiovascular pressure metrics based on the measured
cardiovascular pressure signal, wherein the plurality of
cardiovascular metrics includes at least one cardiovascular
pressure metric indicative of a timing of at least one cardiac
pulse, means for determining a metric indicative of a timing of at
least one heart depolarization within the measured electrical
depolarization signal, means for comparing the timing of the at
least one cardiac pulse to the timing of the at least one
depolarization signal, and means for determining whether to discard
the plurality of cardiovascular pressure metrics based on whether
the timings substantially agree.
[0010] In another example, a method comprises measuring, by a first
pressure sensor, a first cardiovascular pressure signal, and
determining a plurality of first cardiovascular pressure metrics
based on the measured first cardiovascular pressure signal, wherein
the plurality of first cardiovascular metrics includes at least one
first cardiovascular pressure metric indicative of a timing of at
least one cardiac pulse. The method further comprises measuring, by
a second pressure sensor that is coupled to the first pressure
sensor, a second cardiovascular pressure signal, and determining at
least one second cardiovascular pressure metric based on the
measured second cardiovascular pressure signal, wherein the at
least one second cardiovascular pressure metric is indicative of a
timing of at least one cardiac pulse. The method further comprises
comparing the timing of the at least one cardiac pulse indicated by
the first cardiovascular pressure metric to the timing of the at
least one cardiac pulse indicated by the second cardiovascular
pressure metric, and determining whether to discard the plurality
of first cardiovascular pressure metrics based on whether the
timings substantially agree.
[0011] In another example, a system comprises a first pressure
sensor configured to measure a first cardiovascular pressure
signal, a second pressure sensor configured to measure a second
cardiovascular pressure signal, wherein the first and second
pressure sensors communicate with each other, and one or more
analysis modules implemented in one or more of the first and second
pressure sensors. The one or more analysis modules are configured
to determine a plurality of first cardiovascular pressure metrics
based on the measured first cardiovascular pressure signal, wherein
the plurality of first cardiovascular metrics includes at least one
first cardiovascular pressure metric indicative of a timing of at
least one cardiac pulse, determine at least one second
cardiovascular pressure metric based on the measured second
cardiovascular pressure signal, wherein the at least one second
cardiovascular pressure metric is indicative of a timing of at
least one cardiac pulse, compare the timing of the at least one
cardiac pulse indicated by the first cardiovascular pressure metric
to the timing of the at least one cardiac pulse indicated by the
second cardiovascular pressure metric, and determine whether to
discard the plurality of first cardiovascular pressure metrics
based on whether the timings substantially agree.
[0012] In another example, a method comprises measuring, by a
medical device that is coupled to a pressure sensor, an electrical
depolarization signal of the heart, detecting asystole based on the
electrical depolarization signal of the heart, and, in response to
the detection of asystole, directing the pressure sensor to measure
a cardiovascular pressure signal.
[0013] In another example, a system comprises a pressure sensor and
a medical device. The medical device is configured to measure an
electrical depolarization signal of the heart, detect asystole
based on the electrical depolarization signal of the heart, and in
response to the detection of asystole, directing the pressure
sensor to measure a cardiovascular pressure signal.
[0014] The details of one or more aspects of the disclosure are set
forth in the accompanying drawings and the description below. Other
features, objects, and advantages will be apparent from the
description and drawings, and from the claims.
BRIEF DESCRIPTION OF DRAWINGS
[0015] FIGS. 1A and 1B are conceptual diagrams illustrating example
systems that may be used to provide therapy to and/or monitor a
heart of a patient.
[0016] FIG. 2 is a conceptual diagram of a human heart, including
an example pressure sensor.
[0017] FIG. 3 is a functional block diagram illustrating an example
configuration of an IMD that may be used to implement certain
techniques of this disclosure.
[0018] FIG. 4 is a functional block diagram illustrating an example
configuration of a pressure sensor that may be used to implement
certain techniques of this disclosure.
[0019] FIG. 5 is a timing diagram showing a conceptual signal
indicative of pulmonary arterial pressure (PAP), and a conceptual
cardiac electrogram signal, e.g., ECG, signal for the same
period.
[0020] FIG. 6 is a timing diagram showing a signal indicative of
pulmonary arterial pressure, and an ECG for the same period, in
accordance with certain techniques of this disclosure.
[0021] FIG. 7 is a flow diagram illustrating an example method for
operating a pressure sensor coupled with an implantable medical
device (IMD), in accordance with various techniques of this
disclosure.
[0022] FIG. 8 is a flow diagram illustrating an example method for
operating an implantable medical device coupled with a pressure
sensor, in accordance with various techniques of this
disclosure.
[0023] FIG. 9 is a decision tree describing an example comparison
of a pulse rate and a heart rate, in accordance with various
techniques of this disclosure.
[0024] FIG. 10 is a flow diagram illustrating an example technique
for verifying cardiovascular pressure metrics based on a comparison
signals from two pressure sensors.
[0025] FIG. 11 is a flow diagram illustrating an example method
that may be implemented by an IMD, or other device, to determine
when to control a pressure sensor to measure a cardiovascular
pressure signal and determine cardiovascular pressure metrics.
[0026] FIG. 12 is a block diagram illustrating an example system
that includes a server and one or more computing devices that are
coupled to an IMD and a programmer.
DETAILED DESCRIPTION
[0027] This disclosure describes various techniques for verifying
cardiovascular pressure metrics obtained through cardiovascular
pressure monitoring. Heart rate is often measured by sensing
ventricular electrical depolarizations from an electrocardiogram
(ECG) or intracardiac electrogram (EGM). Sensing the electrical
activity of the heart may be performed by IMDs or external
monitoring devices. Thus, although in many of the examples
described herein sensing of electrical activity of the heart is
done by an IMD, in other examples an external medical device may
sense electrical activity of the heart and perform the various
techniques described herein with respect to an IMD. Pulse rate and
other cardiovascular pressure metrics, such as systolic pressure
and diastolic pressure, may be derived from a cardiovascular
pressure signal from one or more pressure sensors in the pulmonary
artery, aorta, atria, ventricle, or other locations within the
cardiovascular system. The measured cardiovascular pressure may be
subject to interference from pressure fluctuations due, for
example, to respiration, wave reflection, motion, and coughing.
Using the techniques of this disclosure, the cardiovascular
pressure metrics determined from the cardiovascular pressure signal
may be verified by a comparison with a cardiac electrical metric,
such as a heart rate, obtained from a measured electrical
depolarization signal.
[0028] FIG. 1A is a conceptual diagram illustrating an example
system 10A that may be used to monitor and/or provide therapy to
heart 200 of patient 100. Patient 100 will ordinarily, but not
necessarily, be a human. System 10 includes IMD 102A (generically
"IMD 102"), which is coupled to leads 106, 108, and 110, and
programmer 104. IMD 102A may be, for example, an implantable
pacemaker, cardioverter, and/or defibrillator that senses
electrical signals of heart 200, and provides electrical signals to
heart 200, via electrodes coupled to one or more of leads 106, 108,
and 110. In accordance with certain techniques of this disclosure,
IMD 102A may receive pressure information from a pressure sensor
114 located within, for example, pulmonary artery 208 of patient
100 and, in some examples, provide therapeutic electrical signals
to heart 200 based on the received pressure information. Pressure
sensor 114 may be coupled to IMD 102 via a lead, or wirelessly. In
some examples, IMD 102A may control pressure sensor 114 to make one
or more pressure measurements in response to the detection of an
arrhythmia in the heart of patient 100. The pressure measurements
performed by pressure sensor 114 may be used to verify the
arrhythmia or refine the diagnosis or treatment of the condition by
IMD 102B.
[0029] Leads 106, 108, 110 extend into the heart 200 of patient 100
to sense electrical activity of heart 200 and/or deliver electrical
stimulation to heart 200. In the example shown in FIG. 1A, right
ventricular lead 106 extends through one or more veins (not shown),
the superior vena cava (not shown), and right atrium 204, and into
right ventricle 202. Left ventricular coronary sinus lead 108
extends through one or more veins, the vena cava, right atrium 204,
and into the coronary sinus 212 to a region adjacent to the free
wall of left ventricle 206 of heart 200. Right atrial lead 110
extends through one or more veins and the vena cava, and into the
right atrium 204 of heart 200.
[0030] IMD 102A may sense electrical signals attendant to the
depolarization and repolarization of heart 200 via electrodes (not
shown in FIG. 1A) coupled to, for example, at least one of the
leads 106, 108, 110. In some examples, IMD 102A provides pacing
pulses to heart 200 based on the electrical signals sensed within
heart 200. The configurations of electrodes used by IMD 102A for
sensing and pacing may be unipolar or bipolar. IMD 102A may also
provide defibrillation therapy and/or cardioversion therapy via
electrodes located on at least one of the leads 106, 108, 110. IMD
102A may detect arrhythmia of heart 200, such as fibrillation of
ventricles 202 and 206, and deliver defibrillation therapy to heart
200 in the form of electrical pulses. In some examples, IMD 102A
may be programmed to deliver a progression of therapies, e.g.,
pulses with increasing energy levels, until a fibrillation of heart
200 is stopped. IMD 102A detects fibrillation by employing one or
more fibrillation detection techniques known in the art. The number
and configuration of electrodes and leads is merely an example and
IMD 102A may be coupled to more or fewer electrodes and leads. In
some configurations, IMD 102A may include an integral or housing
electrode, which may facilitate unipolar delivery of electrical
signals or sensing via a combination of one or more of the
electrodes on the leads and the housing electrode.
[0031] In some examples, programmer 104 may be a handheld computing
device or a computer workstation. A user, such as a physician,
technician, or other clinician, may interact with programmer 104 to
communicate with IMD 102A. For example, the user may interact with
programmer 104 to retrieve physiological or diagnostic information
from IMD 102A. A user may also interact with programmer 104 to
program IMD 102A, e.g., select values for operational parameters of
the IMD.
[0032] For example, the user may use programmer 104 to retrieve
information from IMD 102A regarding the rhythm of heart 200, trends
therein over time, or arrhythmic episodes. As another example, the
user may use programmer 104 to retrieve information from IMD 102A
regarding other sensed physiological parameters of patient 100,
such as intracardiac or intravascular pressure, activity, posture,
respiration, or thoracic impedance. As another example, the user
may use programmer 104 to retrieve information from IMD 102A
regarding the performance or integrity of IMD 102A or other
components of system 10A, such as leads 106, 108 and 110, pressure
sensor 114, or a power source of IMD 102A. The user may use
programmer 104 to program a therapy progression, select electrodes
used to deliver defibrillation pulses, select waveforms for the
defibrillation pulse, or select or configure a fibrillation
detection algorithm for IMD 102A. The user may also use programmer
104 to program aspects of other therapies provided by IMD 102A,
such as cardioversion or pacing therapies.
[0033] IMD 102A and programmer 104 may communicate via wireless
communication using any technique known in the art. Examples of
communication techniques may include, for example, low frequency or
radiofrequency (RF) telemetry, but other techniques are also
contemplated. In some examples, programmer 104 may include a
programming head that may be placed proximate to the patient's body
near the IMD 102A implant site in order to improve the quality or
security of communication between IMD 102A and programmer 104.
[0034] FIG. 1B is a conceptual diagram illustrating another example
system 10B that may be used to monitor and/or provide therapy to
heart 200 of patient 100. System includes IMD 102B (generically
`IMD 102`) with integral electrodes 116 and 118, e.g. housing
electrodes, programmer 104, and a pressure sensor 114. In some
configurations, IMD 102B may have two or more housing electrodes.
IMD 102B may be, for example, an implantable monitor that monitors
electrical signals of heart 200, e.g., senses electrical signals
attendant to the depolarization and repolarization of heart 200,
via electrodes 116.
[0035] IMD 102B may include additional sensors, such as an
accelerometer for monitoring patient posture or activity. In some
examples, IMD 102B may be implemented in, or similar to, a
Reveal.RTM. implantable monitor, available from Medtronic, Inc. of
Minneapolis, Minn. In other examples, IMD 102B may be configured to
provide a therapy, such as providing therapeutic electrical
stimulation via electrodes 116 or 118. In some examples, IMD 102B
may implanted proximate to or within target tissue for the therapy,
such as within a chamber of the heart to which IMD 102B may deliver
cardiac pacing.
[0036] In accordance with certain techniques of this disclosure,
IMD 102B may wirelessly receive pressure information from pressure
sensor 114 located within, for example, pulmonary artery 208 of
patient 100. In some examples, IMD 102B may store the pressure
information and/or relay the pressure information to another
device, e.g., programmer 104. In some examples, IMD 102B may
diagnose a patient condition based, at least in part, on pressure
information received from pressure sensor. In some examples, IMD
102B may provide therapeutic electrical signals to heart 200 based
on the received pressure information. In further examples, IMD 102B
may control pressure sensor 114 to take one or more pressure
measurements in response to the detection of an arrhythmia in the
heart of patient 100. The pressure measurements performed by
pressure sensor 114 may be used to verify the arrhythmia or refine
the diagnosis or treatment of the condition by IMD 102B.
[0037] As shown in FIG. 2, pressure sensor 114 may be a leadless
assembly, e.g., need not be physically coupled to an IMD or other
device via a lead, and need not otherwise be coupled to any leads.
Although not depicted, pressure sensor 114 may include wireless
communication capabilities such as low frequency or radiofrequency
(RF) telemetry, or other wireless communication techniques that
allow sensor 114 to communicate with IMD 102B, programmer 104, or
another device. Pressure sensor 114 may be located in the pulmonary
artery 208, right ventricle 202, aorta, and other locations within
the pulmonary and systemic circulatory systems of patient 100.
Pressure sensor 115 may be affixed to the wall of the pulmonary
artery 208 or, as another example, the wall of the right ventricle
202, using any number of well-known techniques. For example,
pressure sensor 208 may include fixation elements, e.g., helical
tines, hooked tines, barbs, or the like, that allow sensor 114 to
be secured to tissue at a desired location. In other examples,
pressure sensor 114 may be attached to a stent having any variety
of conformations, for example, and the stent/sensor combination may
be implanted within pulmonary artery 208.
[0038] Pressure sensor 114 may be implanted within pulmonary artery
208 or in other locations within the pulmonary or systemic
circulatory systems of patient 100 by, for example, using a
delivery catheter. For example, a physician may deliver pressure
sensor(s) 114 via a delivery catheter, transvenously through either
the internal jugular or femoral veins. The delivery catheter then
extends through superior vena cava 218, right atrioventricular
valve 220, right ventricle 202, and pulmonary valve 222 into
pulmonary artery 208. In other examples, pressure sensor 114 may be
implanted after a physician has opened the chest of the patient by
cutting through the sternum, or via an open-heart procedure, which
may be similar to a valve replacement surgery.
[0039] Pressure sensor 114 generates a pressure signal as a
function of the fluid pressure in, for example, pulmonary artery
208. An IMD 102, programmer 104, and/or another device, e.g.,
external monitoring equipment, may receive a cardiac cycle length
(or pulse rate or pulse-to-pulse intervals) and/or other
cardiovascular pressure metrics transmitted by pressure sensor 114.
In other examples, pressure sensor 114 may receive cardiac
depolarization data or other electrical metrics from an IMD 102 for
comparison purposes.
[0040] More generally, the techniques for verifying cardiovascular
pressure metrics described herein may be implemented in an IMD 102,
pressure sensor 114, programmer 24, another computing device, such
as a remote server, or any combination of such devices. In some
example implementations, one or more pressure sensors 114 may
communicate a cardiovascular pressure signal to another device,
e.g., IMD 102, which may determine one or more cardiovascular
pressure metrics based on the signal. In other examples, one or
more pressure sensors 114 may determine cardiovascular pressure
metrics based on the signal, and transmit the pressure metrics to
one or more other devices, e.g., IMD 102. In some examples, IMD 102
may compare a cardiovascular pressure metric to a corresponding
cardiac electrical metric for verification of one or more other
cardiovascular pressure metrics. In other examples, pressure sensor
114 or another device may receive the electrical metric from IMD
102 for comparison to the corresponding cardiovascular pressure
metric and verification of other cardiovascular pressure metrics.
In a further example, as will be described in greater detail below,
one or more pressure sensors 114 may compare and verify
cardiovascular pressure metrics received from one or more other
pressure sensors 114.
[0041] FIG. 3 is a functional block diagram illustrating an example
configuration of an IMD 102 that may be used to implement certain
techniques of this disclosure. In the illustrated example, IMD 102A
includes a processor 320, memory 322, signal generator 324, sensing
module 326, communication module 328, and pressure analysis module
330. As seen in FIG. 3, one or more pressure sensors 114 may be in
communication with IMD 102 via communication module 328. In the
illustrated example, IMD 102 is coupled to electrodes 328A-328K
("electrodes 328"), which may correspond to the electrodes on leads
106, 108 and 110 coupled to IMD 102A (FIG. 1A) and an integral
electrode on the housing of IMD 102A, or to integral electrodes,
e.g., electrodes 116 and 118 (FIG. 1B), as shown with IMD 102B in
FIG. 1B. IMD 102 may, in some examples, be coupled to more or fewer
electrodes 328.
[0042] In some examples, analysis module 330 analyzes the
cardiovascular pressure signal or metrics received from pressure
sensor(s) 114. Analysis module 330 may be implemented as software,
firmware, hardware, or any combination thereof. In some example
implementations, analysis module 330 may be a software process
implemented in or executed by processor 320. Memory 322 is one
example of a non-transistory, computer-readable storage medium that
includes computer-readable instructions that, when executed by
processor 320, cause IMD 102 and processor 320 to perform various
functions attributed to IMD 102 and processor 320 in this
disclosure. Memory 322 may include any volatile, non-volatile,
magnetic, optical, or electrical media, such as a random access
memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM),
electrically-erasable programmable ROM (EEPROM), flash memory, or
any other digital or analog media.
[0043] In some example implementations, processor 320 of IMD 102
may control signal generator 324 to deliver stimulation therapy to
heart 200 based on the determined cardiac cycle length or various
cardiovascular pressure metrics. For example, upon receiving a
systolic pressure from pressure sensor 114, analysis module 330 may
determine that the systolic pressure in the pulmonary artery is
below a predetermined threshold value. In response, processor 320
may, for example, control signal generator 324 to deliver pacing
pulses to heart 200 to increase the amount of blood flow. Processor
320 may also adjust pacing settings in response to the
determination. For example, processor 320 may adjust one or more
atrioventricular or interventricular delays for pacing therapy,
e.g., cardiac resynchronization therapy. In some examples, a
clinician or an external or implantable medical device may deliver
a drug or other therapy based on the determined cardiac cycle
length and/or various cardiovascular pressure metrics.
[0044] Processor 320 may include any one or more of a
microprocessor, a controller, a digital signal processor (DSP), an
application specific integrated circuit (ASIC), a
field-programmable gate array (FPGA), or equivalent discrete or
analog logic circuitry. In some examples, processor 80 may include
multiple components, such as any combination of one or more
microprocessors, one or more controllers, one or more DSPs, one or
more ASICs, or one or more FPGAs, as well as other discrete or
integrated logic circuitry. The functions attributed to processor
320 in this disclosure may be embodied as software, firmware,
hardware or any combination thereof.
[0045] In some examples, processor 320 controls signal generator
324 to deliver stimulation therapy to heart 200 according to a
selected one or more of therapy programs, which may be stored in
memory 322. For example, processor 320 may control signal generator
324 to deliver electrical pulses with the amplitudes, pulse widths,
frequency, or electrode polarities specified by the selected one or
more therapy programs.
[0046] Signal generator 324 may be electrically coupled to
electrodes 328, e.g., via conductors of, for example, the
respective leads 106, 108, 110 of FIG. 1A, or, in the case of
integral electrodes such as integral electrodes 116 and 118, via an
electrical conductor disposed within housing of IMD 102. In some
examples, signal generator 324 is configured to generate and
deliver electrical stimulation therapy to heart 200. In some
examples, signal generator 324 delivers pacing, cardioversion, or
defibrillation stimulation in the form of electrical pulses. In
other examples, signal generator 324 may deliver one or more of
these types of stimulation in the form of other signals, such as
sine waves, square waves, or other substantially continuous time
signals, or one or more specified duration bursts of such
continuous signals.
[0047] Signal generator 324 may include a switch module, and
processor 320 may use the switch module to select which of the
available electrodes are used to deliver such stimulation. The
switch module may include a switch array, switch matrix,
multiplexer, or any other type of switching device suitable to
selectively couple stimulation energy to selected electrodes.
[0048] In some examples, sensing module 326 monitors signals from
at least one of electrodes 328 in order to monitor electrical
activity of heart 200. Sensing module 326 may also include a switch
module. In some examples, processor 320 may select the electrodes
that function as sense electrodes via the switch module within
sensing module 326.
[0049] Sensing module 326 may include one or more detection
channels (not shown), each of which may comprise an amplifier. The
detection channels may be used to sense the cardiac signals. Some
detection channels may detect cardiac events, such as R- or
P-waves, and provide indications of the occurrences of such events
to processor 320. One or more other detection channels may provide
the signals to an analog-to-digital converter, for processing or
analysis by analysis module 330. In some examples, analysis module
330 may store the digitized versions of signals from one or more
selected detection channels in memory 322 as EGM signals. In
response to the signals from processor 320, the switch module
within sensing module 326 may couple selected electrodes to
selected detection channels, e.g., for detecting events or
acquiring an EGM in a particular chamber of heart 200.
[0050] In some cases, it may be desirable for IMD 102 or other
devices to have cardiovascular pressure metrics for patient 100.
However, due to constraints regarding the size or location of
devices, it may be not desired to have a pressure sensor included
as part of IMD 102 or coupled to IMD 102 via a lead. Accordingly,
cardiovascular pressure metrics such as peak-systolic pressure and
end-diastolic pressure may be derived from the cardiovascular
pressure from one or more wireless pressure sensors 114 in the
pulmonary artery or other locations in the patient's circulatory
system.
[0051] As illustrated in FIG. 3, in addition to program
instructions, memory 322 may store a cardiovascular metric or other
data, e.g., cardiovascular signals, received from pressure sensor
114 via communication module 328. Raw data, such as a
cardiovascular pressure signal may be stored in memory 322 as
pressure data 334 to be processed by analysis module 330. Processor
320 may store cardiovascular metrics processed by analysis module
330, or by pressure sensors 114, in memory 322 as processed data
332. Processed data 332 may represent metrics such as cycle
lengths, pulse rates, peak-systolic pressure, end-diastolic
pressure, averages or trends therein over time, or other signal
morphology information determined from both the cardiovascular
pressure signals. For example, processed data 332 may include cycle
length data, systolic pressure data, and diastolic pressure data as
processed and/or determined by analysis module 330. In addition, in
some example implementations, processor 320 may order pressure
sensor 114 to measure a pressure within the cardiovascular system
of a patient. For example, based on predetermined timing data
stored in memory 322, or timing data transmitted via a programmer,
e.g., programmer 104, processor 320 may transmit, via communication
module 328, instructions to pressure sensor 114 to take one or more
pressure measurements.
[0052] FIG. 4 is a functional block diagram illustrating an example
configuration of a pressure sensor that may be used to implement
certain techniques of this disclosure. In the illustrated example,
pressure sensor 114 includes a processor 440, analysis module 442,
communication module 444, and memory 446. Processor 440 and
communication module 444 may be similar to processor 320 and
communication module 328 of FIG. 3. Processor 440 may store
pressure information as pressure data 448 and processed data 450 in
memory 446. Pressure data 448 may include raw, unprocessed pressure
information that represents a pressure signal within a pulmonary
artery of a patient. Cardiovascular pressure metrics obtained by
processing the cardiovascular pressure signal may be stored as
processed data 450 in memory 446. In some examples, communication
module 444 may transmit processed data 450 to IMD 102. In other
examples, communication module 444 may transmit pressure data 448
or processed data 450 to programmer 104, or to another external
device, e.g., for further analysis.
[0053] In some examples, analysis module 442 may process a
cardiovascular pressure signal sensed by pressure sensor 114 and
store the processed information in memory 446 as processed data
450. Analysis module 442 may be implemented as software, firmware,
hardware or any combination thereof. In some example
implementations, analysis module 442 may be a software process
implemented in or executed by processor 440. Processed data 450 may
represent the cardiovascular metrics determined based on pressure
data 448, such as cycle lengths, averages, trends over time. In
particular, processed data 450 may include cycle length data,
cardiac pulse rate, systolic pressure, diastolic pressure, or other
signal morphology information as processed and/or determined by
analysis module 442. Communication module 444 may transmit
processed data 442 to IMD 102, programmer 104, or another external
device for further analysis.
[0054] In some examples, processor 320 of IMD 102 or processor 440
of pressure sensor 114 may compare a detected cardiac pulse
interval or pulse rate measured via pressure sensor 114 to a
cardiac depolarization interval or rate of heart 200 measured via
an electrodes 328 connected to IMD 102. Comparing the cardiac
depolarization timing to the cardiac pulse timing in this manner
allows for a verification of the cardiovascular metrics obtained by
analyzing the cardiovascular pressure signal.
[0055] Comparing depolarization and pulse rates or intervals in
this manner may save communication bandwidth and power by allowing
for the verification of cardiovascular metrics obtained for a
particular time span. The comparison of these metrics enables
either processor 440 aboard pressure sensor 114 or processor 320
aboard IMD 102 to determine if the cardiovascular pressure metrics
are valid. If the detected cardiac pulse (or pulse rate) and the
detected electric depolarization (or heart rate) do not agree, then
the cardiovascular pressure signal may be experiencing noise and
the resulting metrics may be discarded and the cardiovascular
pressure signal re-measured.
[0056] FIG. 5 is a timing diagram showing a conceptual signal
indicative of pulmonary arterial pressure (PAP), and a conceptual
cardiac electrogram signal for the same period. Two complete
cardiac cycles are shown in both tracings. The cardiac electrogram
shows electrical activity of the heart over time. Characteristics
of the cardiac electrogram and PAP signal correspond to a series of
discrete events in the cardiac cycle. For ease of illustration, the
electrogram and PAP signal are conceptual, and include signal
features, some or all of which may be present in discernable in
actual signals detected by devices, e.g., an IMD and pressure
sensor, described herein. Although the example of FIG. 5
illustrates and describes a PAP signal, in other examples a signal
indicative of pressure in another portion of the cardiovascular
system, e.g., a ventricle or aorta, may be sensed by an
appropriately positioned pressure sensor.
[0057] For example, the cardiac electrogram includes five
characteristic waves: Q-wave 500, R-wave 502, S-wave 504, T-wave
506, and P-wave 508, some or all of which may be detectable in a
cardiac electrogram signal sensed by an IMD or external medical
device. At point 510 on the PAP signal the atrioventricular valves
close, blocking fluid communication between the atrium and
ventricle of the heart. At point 512 the pulmonic valve (or aortic
valve if the pressure sensor is disposed on the aorta) opens,
allowing blood to be ejected from the heart, and at point 514 the
pulmonic valve closes again. At point 516 the atrioventricular
valves open while the heart muscles begin to relax. Point 518 marks
the opening of the pulmonic valve and the start of another ejection
period in the cardiac cycle.
[0058] Period 520, stretching from the peak of a P-wave to the peak
of the subsequent R-wave, corresponds to the atrial systole, the
contraction of the atria that drives blood from the atria into the
ventricles. Period 522, from the peak of the R-wave to the opening
of the pulmonic valves, marks a period of isovolumic contraction.
The atrioventricular and pulmonic valves are closed, preventing
blood flow and leading to an increase in pressure in the
ventricles, but that has not yet exceeded the back-pressure in the
pulmonary artery. Period 524, bounded by the opening and closing of
the pulmonic valve is the ejection period of the cardiac cycle.
During ejection period 524 the ventricles contract and empty of
blood, driving the blood into the cardiovascular system. As the
contraction of the ventricles completes, the pressure of the blood
within the cardiovascular system closes the pulmonic valve 514.
Period 526, bounded by the closing of the pulmonic valve 514 and
the opening of the atrioventricular valves 516, is the isovolumic
relaxation of the ventricles. Periods 528 and 530 are collectively
known as the late diastole, where the whole heart relaxes and the
atria fill with blood. Period 528 corresponds to a rapid inflow of
blood while period 530 corresponds to diastasis, the period of
slower flow blood into the atria before the atrial systole 520
occurs again.
[0059] IMD 102 may determine a cardiac depolarization interval or
rate through any of the techniques known in the art. For example,
IMD 102 may detect an electric depolarization by monitoring the
electronic depolarization signal via ECG and determining when the
signal crosses a set threshold corresponding to the detection of an
R-wave. A cardiac depolarization interval or rate may be
determined, for example, by measuring the time period between the
peaks of one or more R-waves. Such rate measurement may also be
achieved by thresholding the 1.sup.st derivative of the cardiac
electrogram, or according to any other technique known in the
art.
[0060] Pressure sensor 114 may determine a cardiovascular pressure
metric through any of the techniques known in the art. For example,
pressure sensor 114 may use pressure analysis module 442 to
calculate the first derivative of the PAP signal. The maximum value
of the first derivative of the PAP signal for a given cardiac cycle
can be used to define the beginning of a window of time and
determine the systolic pressure of the patient via the maximum
pressure within the pulmonary artery in the window. The pressure
sensor may, for example, determine the occurrence of a cardiac
pulse by monitoring the first derivative of the PAP signal for the
sudden spike in pressure, or monitor the second derivative of the
PAP signal for a zero-crossing, corresponding to the beginning of
the expulsion period 524. A cardiac pulse rate may be determined by
measuring the time period between one or more such spikes or
zero-crossings.
[0061] FIG. 6 is a timing diagram showing a signal indicative of
pulmonary arterial pressure, and an ECG for the same period. The
tracings in FIG. 6 represent data taken during the testing of an
implanted pressure sensor. Pressure signal tracing 600 represents
the measured pulmonary artery pressure in mmHg over a span of 14
seconds. ECG tracing 602 represents the measured electrical
depolarization signal for the test subject over the same
period.
[0062] A comparison of pressure signal tracing 600 and ECG tracing
602 demonstrates the connection between the two tracings. For
example, the R-wave in ECG tracing 602, e.g., R-wave 604,
immediately precedes the sharp increase in pressure corresponding
to the beginning of the expulsion phase in pressure signal tracing
600, for example expulsion 606. Each cardiac pulse shown in
pressure signal tracing 600 has a corresponding R-wave spike in ECG
tracing 602.
[0063] Pressure signal tracing 600 shows a pulse rate of
approximately 98 beats per minute, determined by counting the
number of expulsion peaks within the sample time range. Pressure
signal tracing 600 also shows some evidence of mechanical noise.
For example, pressure signal tracing 600 shows a periodic
underlying pattern, represented in periods 608 and 610. The rise
and fall of the maximum pressure in these cycles is repeated in the
remainder of the tracing and may be due to a repetitive activity
such as a respiratory component. The drop in pulmonary artery
pressure at point 612 may be due to a movement or other physical
artifact. Rapid movement or other external factors may produce
sufficient disturbance to distort the measured pressure, possibly
resulting in additional detected or hidden pulses.
[0064] FIG. 7 is a flow diagram illustrating an example method for
operating a wireless pressure sensor coupled with an implantable
medical device, in accordance with various techniques of this
disclosure. Although the example of FIG. 7 is described in the
context of an implantable medical device coupled to the pressure
sensor, in other examples the medical device may be external to the
patient.
[0065] According to the example method, the pressure sensor wakes
from a reduced power consumption state to perform measurements
(702). The pressure sensor measures a cardiovascular pressure
signal (704). The pressure sensor determines a plurality of
cardiovascular metrics based on the measured cardiovascular
pressure signal, including at least one metric related to the
timing of at least one cardiovascular pulse, e.g., a pulse rate or
interval (706). The pressure sensor transmits at least the
cardiovascular pressure metric indicative of the timing of the
cardiovascular pulse to the implanted medical device (708). The
pressure sensor then determines whether the cardiovascular pressure
metrics have been, or should be rejected, e.g., based on an
indication from the implantable medical device (710). The
determination of whether the cardiovascular pressure metrics should
be rejected is based on a comparison of the at least on
cardiovascular pressure metric indicative of pulse timing to
corresponding cardiac depolarization timing. If the cardiovascular
pressure metrics are rejected, the pressure sensor may discard the
cardiovascular pressure metrics, and re-measures the cardiovascular
pressure signal (704) and re-determines the cardiovascular pressure
metrics (706). If the cardiovascular pressure metrics are not
rejected, the pressure sensor returns to a reduced power
consumption sleep state (712).
[0066] In some examples, the pressure sensor, e.g. pressure sensor
114, may spend some or most of its life span in a reduced power
consumption sleep or hibernating state. This allows the pressure
sensor to maximize its battery life. The pressure sensor may wake
from the sleep state (702). Waking may occur automatically on a
fixed schedule, e.g. at certain times of the day, or in response to
an external command, e.g. from linked IMD 102. Such a wake command
may occur over a wire lead, if the pressure sensor is connected to
the IMD through a lead, or wirelessly, e.g. through a signal
received by communication module 444 of pressure sensor 114.
[0067] The pressure sensor, e.g. pressure sensor 114, measures a
cardiovascular pressure signal (704). The raw cardiovascular
pressure signal measured by the pressure sensor may be stored
internally within the pressure sensor, e.g. in memory 446 of
pressure sensor 114, for later analysis. As the pressure measures
the cardiovascular pressure signal, the IMD may measure the
depolarization signal of the heart. In some examples, the pressure
sensor may transmit, e.g. via communication module 444 of pressure
sensor 114, the unprocessed data to an external location, such as
external programmer 104 or IMD 102, for analysis. The pressure
sensor may, in some examples, be located within the pulmonary
artery of the patient's heart. In other examples, the pressure
sensor may be located in other arteries of the cardiovascular
system, the aorta, or a ventricle, e.g., the right ventricle.
[0068] The pressure sensor, in some examples, determines a
plurality of cardiovascular pressure metrics based on the measured
cardiovascular pressure signal, including at least one metric
indicative of the timing of a cardiovascular pulse (706). The
pressure sensor, e.g. pressure sensor 114, analyzes, e.g. via
analysis module 442 of pressure sensor 114, the measured
cardiovascular signal to determine the cardiovascular pressure
metrics, which may include a cardiac pulse interval or rate.
Example representative cardiovascular metrics include the cardiac
pulse rate, interval or cycle length, systolic pressure, or
diastolic pressure. As pressure sensor determines the
cardiovascular pressure metric indicative of cardiac pulse timing,
e.g., pulse interval, cycle length, or rate, the IMD may determine
a corresponding depolarization timing metric based on the
depolarization signal, e.g., a depolarization interval, cycle
length, or rate.
[0069] In some examples, detecting a cardiac pulse allows the
pressure sensor, IMD, or an external programmer, e.g. programmer
104, to perform a beat-to-beat comparison of the measured
cardiovascular pressure signal, representative cardiovascular
pressure metrics and any depolarization data or metric collected by
other sensors, e.g. by electrodes 328. However, to avoid power
consumption and complexity that may be associated with a
beat-to-beat comparison, the pressure sensor may determine a
cardiovascular pressure metric indicative of pulse timing. This
allows the system to determine and verify the representative
cardiovascular metrics over a longer period, limiting the number of
communication exchanges with an IMD or external programmer.
[0070] In some examples, the pressure sensor transmits the
cardiovascular pressure metrics to the IMD (708). This
communication may occur over a lead, in examples where the pressure
sensor is connected to the IMD via a lead. In many examples, it is
beneficial for the patient's health that the number of leads is
minimized and communication between the pressure sensor and the IMD
may take place wirelessly. In either example, the pressure sensor
may use a communication module, e.g. communication module 444 of
pressure sensor 114, to control communications.
[0071] In some examples, the pressure sensor may transmit the
unprocessed cardiovascular signal measured by the pressure sensor
to the IMD or an external programmer for further processing.
However, such data transmission may be undesired in terms of power
consumption, and in some examples the pressure sensor may transmit
only the determined cardiovascular pressure metrics to the IMD for
further use. The transmission link aboard the pressure sensor may
also serve to receive commands from the IMD, such as a wake or
sleep command. Data or representative metrics measured by the IMD
may be transmitted to the pressure sensor for further processing.
Upon receipt of the cardiovascular pressure metrics, the IMD or
other device may compare the cardiovascular metric indicative of
cardiac pulse timing with the corresponding depolarization timing
metric to determine if there is substantial agreement between the
two metrics. In situations where the two metrics do not agree, a
re-measurement signal may be transmitted to the pressure sensor
(710).
[0072] The pressure sensor re-measures the cardiovascular pressure
signal in response to discarding the at least one representative
cardiovascular metric (704). The pressure sensor may be required to
discard the detected representative cardiovascular metrics and any
stored cardiovascular pressure signal if the metrics and signal are
determined to be corrupted, e.g. by noise within the cardiovascular
pressure signal. This determination may be made, in some examples,
aboard the IMD, e.g., by processor 32 of IMD 102. The determination
is made, for example, by comparing the cardiac pulse rate to a
depolarization rate, determined from electrically measured
depolarizations of the heart.
[0073] If there is not substantial agreement between the
cardiovascular metric indicative of cardiac pulse timing and the
corresponding depolarization timing metric, the cardiovascular
pressure metrics stored aboard the IMD may be discarded and a
command may be sent to the pressure sensor ordering a
re-measurement. Upon receipt of a re-measurement command, the
pressure sensor may discard the cardiovascular data and metrics
stored within device memory and repeat the measurement of the
cardiovascular pressure signal. The pressure sensor may then
re-determine values of the cardiovascular pressure metrics based on
the re-measured cardiovascular pressure signal and transmit the new
cardiovascular pressure metrics to the IMD.
[0074] In other examples, the pressure sensor may make the
comparison between, for example, a representative pulse rate and
heart rate. The pressure sensor may receive the depolarization rate
or interval from the IMD for comparison with the pulse rate or
interval determined by the pressure sensor based on the sensed
pressure signal. If there is insufficient agreement between the two
values, the cardiovascular pressure metrics and raw cardiovascular
data stored aboard the pressure sensor may be discarded and a
notification may be sent to the IMD indicating that the
cardiovascular metric received by the IMD is potentially in error
and should be discarded. In other examples, the cardiovascular
pressure metrics may not be transmitted by the pressure sensor
until after the comparison, and the determination of whether or not
to transmit the cardiovascular pressure metrics from the pressure
sensor to the IMD may be made based on the results of the
comparison.
[0075] In other examples, IMD may receive the cardiovascular
pressure signal from the pressure sensor and the IMD may determine
the cardiovascular pressure metrics as well as substantial
agreement. In still other examples, another device, e.g.,
programmer 104 or a server, may receive the pulse rate/interval and
depolarization rate/interval and may makes the comparison between
the two sets of metrics and transmit signals to one or both the IMD
and pressure sensor ordering re-measurement if there is significant
disagreement between the metrics.
[0076] In some examples, the pressure sensor may enter a sleep or
hibernation state to conserve battery life (712). The pressure
sensor may enter a sleep state automatically, for example after
completing a set of measurements of the cardiovascular pressure
signal, or in response to an external command, e.g., from IMD 304.
The sleep state may involve a partial shutdown of one or more
components of the pressure sensor as well as inactive components of
the processor controlling the pressure sensor e.g. processor 440 of
pressure sensor 114. Some components of the pressure sensor may
remain active, such as a communication module or a timing circuit,
in order to wake the pressure sensor in order to perform another
set of measurements.
[0077] FIG. 8 is a flow diagram illustrating an example method for
operating an implantable medical device coupled with a wireless
pressure sensor, in accordance with various techniques of this
disclosure. Although illustrated and described in the context of an
IMD, the method of FIG. 8 may, in other examples, be implemented by
an external medical device.
[0078] The pressure sensor wakes from a reduced power consumption
state, e.g., in response to a command from the IMD (802). The IMD
measures an electrical depolarization signal of the heart (804).
The IMD detects the timing of one or more heart depolarizations
within the electrical depolarization signal (806). The IMD receives
at least one representative cardiovascular pressure metric from the
pressure sensor, including metric indicative of cardiovascular
pulse timing (808). The IMD compares the cardiac pulse and
depolarization timings pulse (810), and determines whether there is
substantial agreement between the timings (812). If there is not
substantial agreement, the IMD orders the re-measurement of the
cardiovascular pressure signal (814). If there is substantial
agreement between the timings, e.g., between the intervals, cycle
lengths, or rates, the pressure sensor returns to a reduced power
state once the measurement and re-measurement (if any) procedures
complete (816).
[0079] In some examples, the IMD, e.g. IMD 102, and pressure
sensor, e.g. pressure sensor 114, may spend some or most of its
life span in a reduced power consumption sleep or hibernating
state. This allows the IMD or pressure sensor to maximize its
battery life. The IMD must wake periodically from the sleep state
(802). Waking may occur automatically on a fixed schedule, e.g. at
certain times of the day, or in response to an external command,
e.g. from linked programmer 104. Upon waking, the IMD may transmit
a wake command to the pressure sensor. Such a wake command may
occur over a wire lead, if the pressure sensor is connected to the
IMD through a lead, or wirelessly, e.g. through a signal received
by communication module 444 of pressure sensor 114.
[0080] The IMD measures a depolarization signal of the heart (804).
IMD 102 may measure the depolarization signal through two or more
electrodes 328 connected to sensing module 326 of IMD 102. The
measured depolarization signal may be stored in memory aboard the
IMD, e.g. in memory 322 of IMD 102, for later analysis by the IMD
or an external programmer, such as programmer 104. In some
examples, the IMD may be implanted subcutaneously. As the IMD
measures the depolarization signal, the pressure sensor may measure
the corresponding (e.g., corresponding in time) cardiovascular
pressure signal to enable a comparison or verification of the two
signals.
[0081] The IMD detects the timing of one or more depolarizations
within the electrical depolarization signal (806). The IMD
analyzes, e.g. via analysis module 330 of IMD 102, the electrical
signal measured by the IMD. The IMD detects depolarizations within
the signal. The IMD determines a metric indicative of
depolarization timing, such as an interval between depolarizations,
e.g., a cycle length, or rate of depolarizations. The
depolarization timing metric may be an average of such values, such
as an average of a number of consecutive intervals or an average
rate during a plurality of cardiac cycles.
[0082] The IMD also receives at least one cardiovascular pressure
metric indicative of cardiac pulse timing from the pressure sensor
(808). A cardiovascular pressure metric indicative of cardiac pulse
timing may include one or more of an interval between cardiac
pulses, e.g., a cardiac cycle length, or a pulse rate. The
cardiovascular pressure metric indicative of cardiac pulse timing
may, in some examples, be an average of several such values, such
as an average cycle length or pulse rate over several cardiac
cycles. The IMD may receive the cardiovascular pressure metric
either over a lead, provided the pressure sensor is connected to
IMD via a lead, or wirelessly, e.g., via communication module 328
of IMD 102. The IMD may store the cardiovascular pressure metric in
memory, e.g. in memory 322 of IMD 102.
[0083] In some examples, the IMD may receive unprocessed
cardiovascular pressure data from the pressure sensor. In such
examples, the IMD may process the cardiovascular pressure signal to
determine cardiovascular pressure metrics. The cardiovascular
pressure signal may be stored in memory on IMD.
[0084] The IMD compares the timing of the heart depolarization and
the cardiac pulse, e.g., via processor 320 (810). The IMD orders
the re-measurement of the cardiovascular pressure signal if the
electrical depolarization and cardiac pulse timing do not
substantially agree (814). This command may, in some examples, be
sent when the heart (depolarization) rate and cardiac pulse rate do
not agree. The IMD may also discard any other cardiovascular
pressure metrics, e.g., systolic or diastolic pressures, stored in
local memory that correspond to the failed comparison, e.g., are
based on the same sampling of the cardiovascular pressure signal.
In some examples, the pressure sensor may enter a sleep or
hibernation state to conserve battery life, e.g., upon substantial
agreement of the timing metrics such that the cardiovascular
pressure metrics are accepted and no further measurement is
required (816).
[0085] FIG. 9 is a decision tree describing an example comparison
of a pulse (pressure) rate and a heart (depolarization) rate in
accordance with various techniques of this disclosure. Although the
decision tree of FIG. 9 illustrates an example in which with rates
are compared, in other examples intervals, cycle lengths, or other
metrics representative of the timing of depolarizations and pulses
may be compared.
[0086] In the illustrated example, the IMD, pressure sensor,
programmer, or another computing device compares the heart rate
electrically measured by IMD 102 to a pulse rate received from a
pressure sensor (900). The comparison determines whether the heart
rate and pulse rate are substantially the same (902). If the heart
and pulse rates are substantially the same ("YES" branch of 902),
the comparison module determines that other cardiovascular pressure
metrics determined based on the cardiovascular signal are reliable
(904). The pressure sensor may then enter a sleep mode.
[0087] If the heart rate and pulse rate are not substantially the
same ("NO" branch of 902), the comparison module determines if it
is appropriate to re-measure the cardiovascular pressure signal
(906). If the re-measurement is appropriate, a re-measurement
counter may be updated, a command may be sent to the pressure
sensor to conduct a re-measurement of the cardiovascular signal,
and the process may repeat from step 900 (910). If re-measurement
is not appropriate, the IMD or other device may determine that the
pressure sensor is unable to obtain a verifiable cardiovascular
pressure metric (912). Other processes or algorithms which would
use the cardiovascular pressure metrics may continue to use
previously determined and verified metric values, in some
examples.
[0088] In some examples, the IMD compares the electrically measured
heart rate to a pulse rate received from a pressure sensor (900).
The comparison may be made by a processor, e.g. processor 320 of
IMD 102. The IMD compares the pulse rate to the heart rate measured
over the same time period, e.g., the rates correspond to a common
period of time during which the pressure and depolarization signals
were sampled.
[0089] The verification may include determining whether the heart
rate and pulse rate are substantially the same (902). The agreement
between the two rates may not need to be exact. In some examples,
the agreement between the rates may be within a threshold value of
each other to compensate for minor or anticipated differences in
the identification of depolarizations and pulses by the IMD and
pressure sensor. The threshold value may be a default value, or a
user selectable or programmable value, which may thereby be
patient-specific. In some examples, a patient-specific threshold
may be automatically determined by the IMD or another device
described herein. For example, the IMD or device may monitor
depolarization and pulse rates during a threshold determination
period to identify normal variances in the rates, and set the
threshold accordingly. The threshold determination period may occur
shortly after implantation of one or both of the IMD and pressure
sensor, during a follow-up visit, or periodically. In some
examples, the threshold may dynamically adjust as a function of one
or both of the pulse or depolarization intervals. In any case, if
the heart rate and the cardiac pulse rate agree, the determined
pressure metrics may be verified as reliable (904).
[0090] If the heart rate and cardiac pulse rate do not agree, the
IMD may determine if the cardiovascular pressure signal should be
re-measured (906). In order to conserve battery power, the pressure
sensor and/or IMD may maintain a count of the number of
re-measurements of the cardiovascular pressure signal. If the
number of re-measurements of the cardiovascular pressure signal
exceeds a predetermined threshold, the IMD or pressure sensor may
elect to simply end the re-measurement cycle and conserve power for
other activities. If the predefined threshold has not been
exceeded, the IMD may update the re-measurement count, signal the
pressure sensor to re-measure the cardiovascular pressure signal,
and repeat the verification process from comparison step 900 (910).
In some examples, the re-measurement may be delayed for a set
period, e.g., in order to allow a noise generating condition
affecting the cardiovascular pressure signal to dissipate.
[0091] If the IMD or pressure sensor determines that re-measurement
of the cardiovascular signal is inappropriate, the system may
determine that it cannot obtain verified cardiovascular pressure
metrics (912). The IMD and pressure sensor may take a variety of
actions, including generating an alert, e.g., communicating with an
external device to generate an alert message for the patient or
health care provider, or waiting for another scheduled measurement
cycle. Continuous disagreement between the heart rate and cardiac
pulse rate (or electrical depolarization and cardiac pulse) may
indicate a problem within the system, such as fracture of a lead
carrying an electrode used to detect the electrical depolarizations
of the heart. The disagreement may also indicate that the sensing
threshold parameters of the IMD or the pressure sensor require
adjustment, or that there is a cardiac event, e.g.,
tachyarrhythmia, underway.
[0092] The previous examples included techniques for verifying the
reliability of pressure metrics based on a comparison of a pressure
metric indicative of the timing of cardiac pulses, e.g., the rate
of pulses in the pressure waveform, with the timing of cardiac
depolarizations, e.g., the heart rate determined based on one or
more intervals between consecutively detected R-waves. In some
examples, pressure metrics may be verified based on a comparison of
two cardiovascular signals from two pressure sensors. For example,
first pressure metrics determined based on a first cardiovascular
pressure signal sensed by a first pressure sensor at a first
location within the patient may be verified based on a comparison
with a second pressure metric determined based on a second
cardiovascular pressure signal sensed by a second pressure sensor
at a second location within the patient.
[0093] The comparison may be between first and second metrics
indicative of the timing of cardiac pulses detected within the
first and second waveforms. In some examples, the second
cardiovascular pressure signal from the second pressure sensor may
more reliably include cardiac pulses than the first cardiovascular
pressure signal from the second pressure sensor, e.g., due to the
location of the pressure sensors. For example, the first pressure
sensor may be located outside of the heart of the patient, e.g.,
within the pulmonary artery or aorta, and the second pressure
sensor may be located within the heart of the patient, e.g., within
the right ventricle. The various techniques described herein in the
context of a comparison of pulse and depolarization timing may be
applied to a comparison of pulse timing in first and second
cardiovascular pressure waveforms.
[0094] FIG. 10 is a flow diagram illustrating an example technique
for verifying cardiovascular pressure metrics based on a comparison
signals from two pressure sensors. According to the example of FIG.
10, a first implanted pressure sensor measures a first
cardiovascular pressure signal (920). During the same time period,
e.g., at the same time, a second implanted pressure sensor measures
a second cardiovascular pressure signal (922).
[0095] The first pressure sensor, the second pressure sensor,
and/or one or more other devices determines a first plurality of
cardiovascular pressure metrics based on the first signal and at
least one second cardiovascular pressure metrics based on the
second signal (924). One of the first cardiovascular pressure
metrics is indicative of cardiac pulse timing, e.g., is a first
cardiac pulse rate. The second cardiovascular pressure metrics is
also indicative of cardiac pulse timing, e.g., is a second cardiac
pulse rate.
[0096] The first pressure sensor, the second pressure sensor,
and/or one or more other devices compares the first and second
metrics indicative of cardiac pulse timing (926). If there is not
substantial agreement between the first and second pressure metrics
indicative of timing (NO branch of 928), e.g., according to the
techniques described herein with respect to a
pressure/depolarization comparison, the plurality of first pressure
metrics are rejected by the one or more sensors or other devices.
In some examples, additional second pressure metrics determined
based on the second cardiovascular signal may also be rejected. In
response to the rejection, the first and second pressure sensors
may re-measure the first and second pressure signals, e.g.,
autonomously or in response to a command (920). If there is
substantial agreement between the first and second pressure metrics
indicative of timing (YES branch of 928), e.g., according to the
techniques described herein with respect to a
pressure/depolarization comparison, the plurality of first pressure
metrics are accepted by the one or more sensors or other devices,
e.g., may be stored, presented to a user, or used to determine
treatment of the patient.
[0097] FIG. 11 is a flow diagram illustrating an example method
that may be implemented by an IMD, or other device, to determine
when to control a pressure sensor to measure a cardiovascular
pressure signal and determine cardiovascular pressure metrics. The
example method of FIG. 11 is described, for purposes of
illustration, as being performed by in IMD. According to the
example method, the IMD controls the pressure measurement in
response to detection of a particular heart rate
condition--asystole.
[0098] According to the example method of FIG. 11, the IMD monitors
a cardiac depolarization signal, e.g., to detect R-waves and
determine a heart rate, as described herein (940). The IMD
determines whether asystole is detected (942). For example, the IMD
may detect asystole based on a threshold period of time passing,
such as three seconds, without detecting a cardiac depolarization,
e.g., R-wave. If asystole is not detected (NO branch of 942), the
IMD continues to monitor the cardiac depolarization signal. If
asystole is detected (YES branch of 942), the IMD controls the
pressure sensor to measure a cardiovascular pressure signal and
determine one or more cardiovascular pressure metrics based on the
pressure signal (944). The IMD, or another device, may use the
pressure metrics to confirm the asystole, e.g., determine whether
there is truly an absence of depolarizations or whether the IMD did
not sense depolarizations that occurred. The determination may be
based on the presence or absence of cardiac pulses in the pressure
signal. Modification of depolarization sensing, storage of an
episode (which may include the depolarization and pressure
waveforms, or delivery of a therapy, e.g., pacing, cardioversion,
or defibrillation, may be performed by one or more devices based on
the one or more pressure metrics confirming or denying the detected
asystole.
[0099] FIG. 12 is a block diagram illustrating an example system
1000 that includes an external device, such as a server 1012, and
one or more computing devices 1016A-1016N, that are coupled to the
IMD 102 and programmer 104 via a network 1010. In this example, IMD
102 may use a communication module, e.g. communication module 328,
to communicate with programmer 104 via a first wireless connection,
and to communication with an access point 1018 via a second
wireless connection. In the example of FIG. 12, access point 1018,
programmer 104, server 1012, and computing devices 1016A-1016N are
interconnected, and able to communicate with each other, through
network 1010. In some cases, one or more of access point 1018,
programmer 104, server 1012, and computing devices 1016A-1016N may
be coupled to network 1010 through one or more wireless
connections. IMD 102, programmer 104, server 1012, and computing
devices 1016A-1016N may each comprise one or more processors, such
as one or more microprocessors, DSPs, ASICs, FPGAs, programmable
logic circuitry, or the like, that may perform various functions
and operations, such as those described herein.
[0100] Access point 1018 may comprise a device that connects to
network 1010 via any of a variety of connections, such as telephone
dial-up, digital subscriber line (DSL), or cable modem connections.
In other examples, access point 1018 may be coupled to network 1010
through different forms of connections, including wired or wireless
connections. In some examples, access point 1018 may be co-located
with the patient, e.g. patient 10, and may comprise one or more
programming units and/or computing devices (e.g., one or more
monitoring units) that may perform various functions and operations
described herein. For example, access point 1018 may include a
home-monitoring unit that is co-located with the patient and that
may monitor the activity of IMD 102.
[0101] In some cases, server 1012 may be configured to provide a
secure storage site for data that has been collected from IMD 102
and/or programmer 104. Network 1010 may comprise a local area
network, wide area network, or global network, such as the
Internet. In some cases, programmer 104 or server 1012 may assemble
data in web pages or other documents for viewing by trained
professionals, such as clinicians, via viewing terminals associated
with computing devices 1016A-1016N. The illustrated system of FIG.
10 may be implemented, in some aspects, with general network
technology and functionality similar to that provided by the
Medtronic CareLink.RTM. Network developed by Medtronic, Inc., of
Minneapolis, Minn.
[0102] In some examples, processor 1020 of server 1012 may be
configured to receive pressure information from a pressure
sensor(s), e.g., pressure sensor 114, and/or depolarization
information from an IMD, e.g., IMD 102, for processing by analysis
module 1022 in the manner described throughout this disclosure.
Analysis module 1022 may determine cycle lengths, rates, systolic
pressures, and/or diastolic pressures based on the received
information using any of the techniques described in this
disclosure. Processor 1020 may compare rate, cycle lengths, or any
other metrics indicative of the timing of depolarizations and
pulses, using any of the techniques described herein, in order to
verify the reliability of one or more cardiovascular pressure
metrics.
[0103] Processor 1020 may provide alerts to users, e.g., to the
patient via access point 1018 or to a clinician via one of
computing devices 1016, identifying change, e.g., worsening, in
patient condition based on cardiac cycle length and/or pressure
metrics measured from pulmonary arterial pressures. Processor 1020
may suggest to a clinician, e.g., via programmer 104 or a computing
device 1016, a change in a therapy, such as CRT, based on cardiac
cycle length and/or pressure metrics measured from pulmonary
arterial pressures. Processor 1020 may also adjust or control the
delivery of therapy by IMD 102, e.g., electrical stimulation
therapy and/or a therapeutic substance, via network 1010.
[0104] In some examples, using the various techniques described
above, cardiovascular pressure metrics obtained from a remotely
located pressure sensor may be verified based on a measured
electrical depolarization signal of the heart without requiring
additional leads implanted into the patient. The cardiovascular
pressure measurements and verification may be periodic, e.g.,
hourly or daily. In some examples, the compared depolarization and
pulse timing metrics may be averages over a number of cardiac
cycles, e.g., average pulse and depolarization rates.
[0105] In some examples, the IMD may perform a beat-to-beat
verification of the pressure metrics transmitted by the pressure
sensor. The beat-to-beat verification may be performed periodically
for a period of time, or continuously. The beat-to-beat
verification may be a beat-to-beat comparison of average timing
metrics, or may include verifying that an individual detected
electrical depolarization of the heart occurred at about the same
time as, or with an expected timing correlation to, the detected
cardiovascular pulse. In the latter examples, the IMD or other
device may verify that each electric depolarization corresponds to
a cardiac pulse, and vice versa, to ensure that the pressure sensor
is not over or under sensing the cardiovascular pressure
fluctuations.
[0106] In some configurations, the pressure sensor may be activated
by the IMD in response to electrically detected cardiac events,
such as an arrhythmia. Cardiovascular pressure metrics provided in
response to such an activation may verify the detection of
arrhythmia by the IMD, or provide useful information for diagnosing
a condition underlying the arrhythmia. In some examples, the
pressure sensor and the IMD may be used in conjunction to provide a
more rapid and accurate diagnosis of specific cardiac events, such
as a premature ventricular contraction (PVC).
[0107] Furthermore, in some examples, the IMD may prompt the
pressure sensor to delay a periodic, e.g., daily, measurement of
cardiovascular pressure. For example, the IMD may prompt the
pressure sensor to delay the measurement in response to detecting a
depolarization rate at which the corresponding cardiac contraction
rate would be such that cardiovascular pressure metrics would be
unreliable.
[0108] Various example implementations of the disclosure have been
described. These and other example implementations are within the
scope of the following claims.
* * * * *